全文获取类型
收费全文 | 4112篇 |
免费 | 531篇 |
国内免费 | 250篇 |
专业分类
化学 | 1126篇 |
晶体学 | 51篇 |
力学 | 1496篇 |
综合类 | 34篇 |
数学 | 816篇 |
物理学 | 1370篇 |
出版年
2024年 | 12篇 |
2023年 | 38篇 |
2022年 | 72篇 |
2021年 | 79篇 |
2020年 | 121篇 |
2019年 | 102篇 |
2018年 | 96篇 |
2017年 | 126篇 |
2016年 | 146篇 |
2015年 | 92篇 |
2014年 | 185篇 |
2013年 | 363篇 |
2012年 | 203篇 |
2011年 | 190篇 |
2010年 | 152篇 |
2009年 | 202篇 |
2008年 | 236篇 |
2007年 | 259篇 |
2006年 | 254篇 |
2005年 | 214篇 |
2004年 | 209篇 |
2003年 | 199篇 |
2002年 | 112篇 |
2001年 | 126篇 |
2000年 | 133篇 |
1999年 | 135篇 |
1998年 | 102篇 |
1997年 | 113篇 |
1996年 | 92篇 |
1995年 | 90篇 |
1994年 | 62篇 |
1993年 | 40篇 |
1992年 | 69篇 |
1991年 | 49篇 |
1990年 | 26篇 |
1989年 | 21篇 |
1988年 | 34篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 4篇 |
1982年 | 16篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有4893条查询结果,搜索用时 15 毫秒
101.
Abstract Experimental investigations have revealed that the Neerfeld–Hill and Eshelby–Kröner models, for grain interactions in massive, bulk (in particular, macroscopically isotropic) polycrystals, and a recently proposed effective grain-interaction model for macroscopically anisotropic polycrystals, as thin films, provide good estimates for the macroscopic (mechanical and) X-ray elastic constants and stress factors of such polycrystalline aggregates. These models can also be used to calculate the strain variation among the diffracting crystallites, i.e. the diffraction-line broadening induced by elastic grain interactions can thus be predicted. This work provides an assessment of diffraction-line broadening induced by elastic loading of polycrystalline specimens according to the various grain-interaction models. It is shown that the variety of environment, and thus the heterogeneity of the stress–strain states experienced by each of the individual grains exhibiting the same crystallographic orientation in a real polycrystal, cannot be accounted for by traditional grain-interaction models, where all grains of the same crystallographic orientation in the specimen frame of reference are considered to experience the same stress–strain state. A significant degree of broadening which is induced by the heterogeneity of the environments of the individual crystallites is calculated on the basis of a finite element algorithm. The obtained results have vast implication for diffraction-line broadening analysis and modelling of the elastic behaviour of massive polycrystals. 相似文献
102.
Y.B. Saddeek 《哲学杂志》2013,93(1):41-54
The elastic properties and Debye temperatures of xB2O3–70TeO2–(30–x)WO3, (0 ≤ x ≤ 30 mol%) glasses have been investigated using sound velocity measurements at 4 MHz. Ultrasonic and thermal parameters, combined with the results of IR spectroscopic analyses, were employed to explore the effect of B2O3 on the structure of tungsten–tellurite glasses. According to IR analysis, there is competition between WO6 and TeO4 units to form BO4 units, and the vibrations of the tellurite structural units are shifted towards lower wavenumbers on the formation of non-bridging oxygens. It is assumed that B2O3 acts as a modifier by decreasing the glass-transition temperature T g and increasing both the thermal stability and glass formation range of the tellurite glasses. The change in density and molar volume with B2O3 content reveals that the borate units are less dense than the tellurite structural units. The observed compositional dependence of elastic moduli is interpreted in terms of the effect of B2O3 on the coordination number of the tellurite units. A good correlation was observed between experimentally determined elastic moduli and those computed with the Makishima–Mackenzie model. 相似文献
103.
天体环境中丰中子核素熔合反应率对研究中子星表面超级暴现象的点火机制有重要意义。由于次级束流强过低,无法使用传统固体靶实验技术测量垒下熔合反应截面。活性靶技术的发展为垒下丰中子核素熔合反应截面的测量提供了可行的途径。基于Geant4模拟详细地分析了多重采样电离室(MUSIC)与时间投影室(TPC)两种活性靶探测器中熔合反应与弹性散射的运动学性质,给出了4种熔合反应鉴别判据,并且计算了由这些判据误判引起的熔合截面系统误差。在Ecm=13.6 MeV时,MUSIC与TPC的弹性散射误判截面分别为0.5 mb和2.9×10-3 mb,都远小于此时熔合截面(877 mb)。在垒下,MSUIC的熔合截面系统误差已经超出实验测量要求,而TPC能够进行实验测量的能量可以降低至Ecm=4.7 MeV。Reaction rates of fusion reactions among neutron-rich nuclei in the astrophysical environment are of great significance to understand the ignition of superbursts on neutron stars. Since beam intensity is rather low for radioactive ion beams, it is extremely difficult to operate a direct measurement for cross sections of such fusion reactions below the Coulomb barrier using thick target technique. In this case, a novel technique, active target technique, has been developed recently. To study the energy limit for measurement below Coulomb barrier, the kinematics of elastic scattering and fusion reaction in MUSIC and TPC are discussed with Geant4 simulation. Four identification methods are used and uncertainties of cross sections resulted from misjudgments are calculated. With Ecm=13.6 MeV, the uncertainties of cross sections for MUSIC and TPC are 0.5 mb and 2.9×10-3 mb, respectively. The uncertainties for MUSIC become far beyond measurement when below coulomb barrier, while TPC remains to be a suitable detector for measuring fusion cross sections until Ecm=4.7 MeV. 相似文献
104.
Hela Ladjimi Dibyendu Sardar Mohamed Farjallah Nisrin Alharzali Somnath Naskar Rym Mlika 《Molecular physics》2018,116(14):1812-1826
In this theoretical work, we calculate potential energy curves, spectroscopic parameters and transition dipole moments of molecular ions BeX+ (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarisation potentials and full configuration interaction. We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion–atom colliding systems by stimulated Raman adiabatic process and discuss the parameters regime under which the population transfer is feasible. Our results are important for ion–atom cold collisions and experimental realisation of cold molecular ion formation. 相似文献
105.
106.
牛顿碰撞球的解释与分析 总被引:1,自引:0,他引:1
对牛顿碰撞球的常规碰撞形式和混合联珠单球碰撞形式做了理论分析和解释.在常规碰撞时,将悬线(钓鱼线)先悬挂小球一段时间后组装仪器,可克服悬线的拉力.在混合联珠单球碰撞时,根据理论分析,选取大球和小球的质量比为27∶8时,演示效果较好. 相似文献
107.
108.
The elastic analysis of a mode II Griffith crack penetrating through a decagonal quasi-crystal along the periodic axis is made within the context of the continuum theory. By using a general solution obtained previously, the problem in the case of uniform shear stress at infinity is solved, and the analytical expressions for the entire stress field disturbed by an internal crack are derived in an explicit form. The asymptotic fields of the displacement and stress around a crack tip in both phonon and phason fields indicate that the stresses near a crack tip exhibit the square-root singularity. The formula for evaluating the energy release rate is also given. If imposing that the phason field is absent, the well-known results of a mode II crack in a conventional material are recovered from the present results. 相似文献
109.
许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的. 相似文献
110.
利用激光干涉测钢丝的杨氏弹性模量 总被引:2,自引:0,他引:2
分析了在洛埃镜干涉装置中等效双狭缝间距变化对干涉条纹密度的影响。导出了钢丝因受力引起的绝对伸长量与干涉条纹密度变化之间的关系 ,并通过它计算了钢丝的杨氏弹性模量。结果表明 ,激光干涉法不仅比光杠杆法测量的量要少 ,而且用该方法通过测微目镜测条纹的位置要比光杠杆法通过望远镜对标尺读数精确 ,其测量结果要比光杠杆法更准确可靠 相似文献